This invention relates to a guide drum apparatus in a magnetic recording and/or reproducing apparatus, more particulary in a video tape recorder.
It is known that in a rotary head type video tape recorder, a rotary head rotating at a high speed records video signals onto and reproduces the same from a running magnetic tape. In order to obtain a stable video image reproduced from recorded video signals, it is required to rotate the rotary magnetic head very smoothly and stably.
However, according to a conventional guide drum apparatus using a d.c. motor with a brush or an a.c. motor, in which the rotational force of the motor is indirectly transferred to the guide drum via a belt, a very smooth and stable rotation of the guide drum cannot be achieved, due e.g. to the poor rotational performance of the motor itself and to the vibration of the belt and/or eccentricity of a pulley.
For overcoming such problems, a directly driven guide drum apparatus has been suggested, in which a common center shaft is used for the motor and the guide drum. Further, a guide drum driven by a brushless motor has been suggested. However, these suggested guide drum arrangements have disadvantages that the leakage fluxes from a rotor of a permanent magnet cause undesired magnetic coupling, i.e. they badly affect the signals recorded on the magnetic tape. For preventing such leakage fluxes, many magnetic shield plates are necessary. Further, the elements used for the motor and the elements used for the guide drum apparatus occupy a considerable space to cause the total apparatus to become big in size. Also, many printed circuit boards are necessary for providing electrical wiring to the many elements in the motor and the guide drum.
Furthermore, for achieving rotational position detection in a brushless motor, a high frequency signal such as several tens kHz is necessarily used, but this high frequency signal is likely to influence the signals in a rotary transformer and the rotary head.